From 7be0ba8cb18e130ee5c108bc0da2bdd651f71ec3 Mon Sep 17 00:00:00 2001
From: Weiqun Zhang <weiqunzhang@lbl.gov>
Date: Tue, 18 Nov 2025 12:16:00 -0800
Subject: [PATCH] RNG on GPU: Assertion it's not in OMP parallel region

RNG on GPU is not OpenMP thread safe.

Thank @AlexanderSinn for pointing this out.
---
 Src/Base/AMReX_RandomEngine.H | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/Src/Base/AMReX_RandomEngine.H b/Src/Base/AMReX_RandomEngine.H
index 6140898be79..6cf2b495dd8 100644
--- a/Src/Base/AMReX_RandomEngine.H
+++ b/Src/Base/AMReX_RandomEngine.H
@@ -4,6 +4,10 @@
 
 #include <AMReX_GpuQualifiers.H>
 #include <AMReX_Extension.H>
+#ifdef AMREX_USE_OMP
+#  include <AMReX_BLassert.H>
+#  include <omp.h>
+#endif
 
 #if defined(AMREX_USE_HIP)
 #pragma clang diagnostic push
@@ -32,8 +36,13 @@ namespace amrex
 
     extern sycl_rng_descr* rand_engine_descr;
 
-    AMREX_FORCE_INLINE
-    sycl_rng_descr* getRandEngineDescriptor () { return rand_engine_descr; }
+    inline
+    sycl_rng_descr* getRandEngineDescriptor () {
+#ifdef AMREX_USE_OMP
+        AMREX_ALWAYS_ASSERT_WITH_MESSAGE(! omp_in_parallel(), "RNG on GPU is not OpenMP thread safe");
+#endif
+        return rand_engine_descr;
+    }
 
     struct RandomEngine {
         sycl_rng_engine* engine;
@@ -52,8 +61,13 @@ namespace amrex
 
     extern randState_t* gpu_rand_state;
 
-    AMREX_FORCE_INLINE
-    randState_t* getRandState () { return gpu_rand_state; }
+    inline
+    randState_t* getRandState () {
+#ifdef AMREX_USE_OMP
+        AMREX_ALWAYS_ASSERT_WITH_MESSAGE(! omp_in_parallel(), "RNG on GPU is not OpenMP thread safe");
+#endif
+        return gpu_rand_state;
+    }
 
     struct RandomEngine {
         randState_t* rand_state;